| Mateusz Dudzinski Limited | Health & social care | 2022 |
| Matrix BPO Ltd | Administrative & support | 2025 |
| Matrix Properties Compliance UK Limited | Construction | 2023 |
| Matt Constructions Ltd | Construction | 2014 |
| Matthews Carpentry Ltd | Manufacturing | 2021 |
| Matthews Companies Ltd | Transport & logistics | 2020 |
| Maven Technology Limited | Information & communication | 2019 |
| Maxone Online Ltd | Wholesale & retail | 2019 |
| Maxtork Controls UK Limited | Professional & scientific | 2023 |
| Maya Traders Ltd | Wholesale & retail | 2022 |
| Mayakumar Holdings Ltd | Wholesale & retail | 2025 |
| Mayfair Business Consultants Ltd | Administrative & support | 2019 |
| Mayfair Escapes Limited | Administrative & support | 2026 |
| Mayfair Productions Ltd | Information & communication | 2019 |
| Maypon Catering & Trading Limited | Wholesale & retail | 2026 |
| Mayz Ltd | Other services | 2024 |
| MB Build & Design Ltd | Construction | 2017 |
| MB Handyman Ltd | Construction | 2025 |
| MB Loft Extensions Ltd | Construction | 2020 |
| MBM Complex Ltd | Households | 2025 |
| MBM Land Holdings Limited | Real estate | 2026 |
| MBO Properties Ltd | Real estate | 2020 |
| MBO Traders Ltd | Administrative & support | 2024 |
| MC Cann & Evans Ltd | Administrative & support | 2013 |
| MC Rendering Services Ltd | Construction | 2007 |
| Mccarthy&Sons Building Ltd | Construction | 2025 |
| Mccready Services Limited | Construction | 2017 |
| Mcluke and Brothers Limited | Real estate | 2025 |
| MCM Direct Construction Limited | Construction | 2022 |
| MD ACS Ltd | Construction | 2023 |
| MD4 Transports Ltd | Transport & logistics | 2024 |
| Mdrh Transport Limited | Transport & logistics | 2017 |
| Mdth Catering Ltd | Hospitality | 2024 |
| Meat Hub Ltd | Wholesale & retail | 2026 |
| Medcev Consulting Limited | Professional & scientific | 2026 |
| Medea 82 Ltd | Transport & logistics | 2019 |
| Medeley Assets Ltd | Real estate | 2025 |
| Medexel SK Ltd | Information & communication | 2025 |
| Medical Imaging and Diagnostics Ltd | Health & social care | 2023 |
| Medicus Consulting Limited | Professional & scientific | 2014 |
| Medique Services Ltd | Administrative & support | 2018 |
| Mediterranean Feltham Ltd | Wholesale & retail | 2026 |
| Mediterranean Technologies Limited | Information & communication | 2022 |
| Medoxon (UK) Ltd | Administrative & support | 2003 |
| Medreich PLC | Wholesale & retail | 1995 |
| Meet Food & Wine Limited | Wholesale & retail | 2008 |
| Mega Saver ST0RE Ltd | Wholesale & retail | 2026 |
| Megarush Ltd | Professional & scientific | 2016 |
| Megatech Services International Ltd | Information & communication | 2021 |
| Megatechitlive Ltd | Information & communication | 2024 |
| Megs Cleaning Service Ltd | Administrative & support | 2024 |
| Mehnaaz Food and Wine Ltd | Wholesale & retail | 2026 |
| Mehta and Sons Ltd | Transport & logistics | 2020 |
| Meiveli Circle CIC | Information & communication | 2022 |
| Meiveli Media Ltd | Information & communication | 2023 |
| Mends Property Company Limited | Real estate | 2020 |
| Mer.Industrial.Ltd Ltd | Professional & scientific | 2023 |
| Merck Cross Border Trustees Limited | Administrative & support | 1967 |
| Merck Holding Ltd. | Financial services | 2013 |
| Merck Investments Limited | Professional & scientific | 2000 |
| Merck Ltd | Professional & scientific | 1967 |
| Merck Pension Trustees Limited | Professional & scientific | 1990 |
| Merck Performance Materials Limited | Manufacturing | 2019 |
| Merck Serono Limited | Wholesale & retail | 1970 |
| Meriva Investment Limited | Households | 2022 |
| Merm Ltd | Transport & logistics | 2022 |
| MESSIAH07 CIC | Other services | 2019 |
| Meta Magna Limited | Information & communication | 2023 |
| Meta Tech Haus Limited | Construction | 2024 |
| Metalhome Construction Ltd | Construction | 2019 |
| Metalprogetti UK Limited | Manufacturing | 2013 |
| Metanoic Retail Services Ltd | Wholesale & retail | 2022 |
| Metric Construction Ltd | Construction | 2013 |
| Metro GAS and Electric Ltd | Administrative & support | 2024 |
| MF Trends Limited | Wholesale & retail | 2026 |
| MFR and MSR Properties Limited | Financial services | 2024 |
| MFR Properties Investment Limited | Real estate | 2021 |
| MG Electrical Services London Ltd | Construction | 2024 |
| MG Logistix Inc. Ltd | Transport & logistics | 2019 |
| MGL Investo Ltd | Real estate | 2024 |
| MGL Recruitment Ltd | Administrative & support | 2025 |
| Mgma Logistics Ltd | Transport & logistics | 2023 |
| Mgmc Chauffeurs Ltd | Transport & logistics | 2026 |
| Miah Industries Ltd | Information & communication | 2022 |
| MIBRAHIM25 Ltd | Wholesale & retail | 2025 |
| Michal M Haulage Ltd | Transport & logistics | 2025 |
| Micholmes Enterprises Limited | Other services | 2014 |
| Micholmes Investments Ltd | Financial services | 2021 |
| Microtronics Limited | Information & communication | 2010 |
| Microwise International Ltd | Construction | 2019 |
| Middle Green Motors (MGM) Limited | Wholesale & retail | 2018 |
| Middx Builds Ltd | Construction | 2025 |
| Midiac Limited | Professional & scientific | 2021 |
| MIE Coach Ltd | Health & social care | 2020 |
| Mikulics & Sons Ltd | Manufacturing | 2025 |
| Milan Pizzeria Ltd | Hospitality | 2025 |
| Milanjaan Capital Ltd | Financial services | 2025 |
| Milbert Financial Services Ltd | Financial services | 2026 |
| Miles Electrical Ltd | Construction | 2023 |
| Milk and Whip Ltd | Manufacturing | 2025 |